adafruit_touchscreen.py

# The MIT License (MIT)
#
# Copyright (c) 2019 ladyada for Adafruit
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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"""
`adafruit_touchscreen`
================================================================================

CircuitPython library for 4-wire resistive touchscreens


* Author(s): ladyada

Implementation Notes
--------------------

**Hardware:**


**Software and Dependencies:**

* Adafruit CircuitPython firmware for the supported boards:
  https://github.com/adafruit/circuitpython/releases
"""

__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_Touchscreen.git"

from digitalio import DigitalInOut
from analogio import AnalogIn


def map_range(x, in_min, in_max, out_min, out_max):
    """
    Maps a number from one range to another.
    Note: This implementation handles values < in_min differently than arduino's map function does.
    :return: Returns value mapped to new range
    :rtype: float
    """
    mapped = (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min
    if out_min <= out_max:
        return max(min(mapped, out_max), out_min)
    return min(max(mapped, out_max), out_min)


class Touchscreen:
    """A driver for common and inexpensive resistive touchscreens. Analog input
    capable pins are required to read the intrinsic potentiometers"""

    def __init__(
        self,
        x1_pin,
        x2_pin,
        y1_pin,
        y2_pin,
        *,
        x_resistance=None,
        samples=4,
        z_threshhold=10000,
        calibration=None,
        size=None
    ):
        """Create the Touchscreen object. At a minimum you need the 4 pins
        that will connect to the 4 contacts on a screen. X and Y are just our
        names, you can rotate and flip the data if you like. All pins must be
        capable of becoming DigitalInOut pins. 'y2_pin', 'x1_pin' and 'x2_pin'
	must also be capable of becoming AnalogIn pins.
        If you know the resistance across the x1 and x2 pins when not touched,
        pass that in as 'x_resistance'.
        By default we oversample 4 times, change by adjusting 'samples' arg.
        We can also detect the 'z' threshold, how much its prssed. We don't
        register a touch unless its higher than 'z_threshold'
        'calibration' is a tuple of two tuples, the default is
        ((0, 65535), (0, 65535)). The numbers are the min/max readings for the
        X and Y coordinate planes, respectively. To figure these out, pass in
        no calibration value and read the raw values out while touching the
        panel.
        'size' is a tuple that gives the X and Y pixel size of the underlying
        screen. If passed in, we will automatically scale/rotate so touches
        correspond to the graphical coordinate system.
        """
        self._xm_pin = x1_pin
        self._xp_pin = x2_pin
        self._ym_pin = y1_pin
        self._yp_pin = y2_pin
        self._rx_plate = x_resistance
        self._xsamples = [0] * samples
        self._ysamples = [0] * samples
        if not calibration:
            calibration = ((0, 65535), (0, 65535))
        self._calib = calibration
        self._size = size
        self._zthresh = z_threshhold

    @property
    def touch_point(self):  # pylint: disable=too-many-locals
        """A tuple that represents the x, y and z (touch pressure) coordinates
        of a touch. Or, None if no touch is detected"""
        with DigitalInOut(self._yp_pin) as y_p:
            with DigitalInOut(self._ym_pin) as y_m:
                with AnalogIn(self._xp_pin) as x_p:
                    y_p.switch_to_output(True)
                    y_m.switch_to_output(False)
                    for i in range(len(self._xsamples)):
                        self._xsamples[i] = x_p.value
        x = sum(self._xsamples) / len(self._xsamples)
        x_size = 65535
        if self._size:
            x_size = self._size[0]
        x = int(map_range(x, self._calib[0][0], self._calib[0][1], 0, x_size))

        with DigitalInOut(self._xp_pin) as x_p:
            with DigitalInOut(self._xm_pin) as x_m:
                with AnalogIn(self._yp_pin) as y_p:
                    x_p.switch_to_output(True)
                    x_m.switch_to_output(False)
                    for i in range(len(self._ysamples)):
                        self._ysamples[i] = y_p.value
        y = sum(self._ysamples) / len(self._ysamples)
        y_size = 65535
        if self._size:
            y_size = self._size[1]
        y = int(map_range(y, self._calib[1][0], self._calib[1][1], 0, y_size))

        z_1 = z_2 = z = None
        with DigitalInOut(self._xp_pin) as x_p:
            x_p.switch_to_output(False)
            with DigitalInOut(self._ym_pin) as y_m:
                y_m.switch_to_output(True)
                with AnalogIn(self._xm_pin) as x_m:
                    z_1 = x_m.value
                with AnalogIn(self._yp_pin) as y_p:
                    z_2 = y_p.value
        # print(z_1, z_2)
        z = 65535 - (z_2 - z_1)
        if z > self._zthresh:
            return (x, y, z)
        return None